1. Field of the Invention
The invention is related to the field of recording head fabrication and, in particular, to improved methods of fabricating perpendicular write elements in perpendicular magnetic recording heads. More particularly, improved methods are discussed to form the write pole and the trailing shield of a perpendicular write element.
2. Statement of the Problem
Magnetic disk drive systems typically include a magnetic disk, a recording head having write and read elements, a suspension arm, and an actuator arm. As the magnetic disk is rotated, air adjacent to the disk surface moves with the disk. This allows the recording head (also referred to as a slider) to fly on an extremely thin cushion of air, generally referred to as an air bearing. When the recording head flies on the air bearing, the actuator arm swings the suspension arm to place the recording head over selected circular tracks on the rotating magnetic disk where signal fields are written to and read by the write and read elements, respectively. The write and read elements are connected to processing circuitry that operates according to a computer program to implement write and read functions.
Magnetic disk drives have typically been longitudinal magnetic recording systems, wherein magnetic data is recorded as magnetic transitions formed longitudinally on a disk surface. The surface of the disk is magnetized in a direction along a track of data and then switched to the opposite direction, both directions being parallel with the surface of the disk and parallel with the direction of the data track.
Unfortunately, data density requirements are fast approaching the physical limits. Overall data density (or areal density) may be improved by improving linear density and/or track density. To improve linear density, bit sizes on a track need to be reduced which in turn requires decreasing the grain size of the magnetic medium. As this grain size shrinks, the magnetic field required to write a bit of data increases proportionally. The ability to produce a magnetic field strong enough to write a bit of data using conventional longitudinal write head technologies is reaching its physical limit.
One way to achieve higher density recordings is with perpendicular recording. In perpendicular recording systems, bits of data are recorded magnetically perpendicular to the plane of the surface of the disk. The magnetic disk may have a relatively high coercivity material at its surface and a relatively low coercivity material just beneath the surface. A write pole having a small cross section and very high magnetic flux emits a strong, concentrated magnetic field perpendicular to the surface of the disk. This magnetic field emitted from the write pole is sufficiently strong to overcome the high coercivity of the surface material and magnetize it in a direction perpendicular to its surface. The magnetic flux then flows through the relatively soft underlayer (SUL) and returns to the surface of the disk at a location adjacent to a return pole of the perpendicular write element. The return pole of the write element typically has a cross section that is much larger than that of the write pole so that the magnetic flux through the disk at the location of the return pole (as well as the resulting magnetic field between the disk and return pole) is sufficiently spread out to render the magnetic flux too weak to overcome the coercivity of the disk surface material. In this way, the magnetization imparted by the write pole is not erased by the return pole.
FIG. 1 illustrates a typical perpendicular write element 100 adapted to write to a perpendicular magnetic recording medium 120. Write element 100 generally includes a yoke 101 comprising a write pole 102 and a return pole 104. Write element 100 also includes a coil wrapped around yoke 101 that is not shown. Perpendicular recording medium 120 includes a perpendicular magnetic recording layer 122 and a soft underlayer (SUL) 124.
When in operation, perpendicular recording medium 120 spins from left to right in FIG. 1. A magnetic flux is generated in yoke 101 due to an electrical current flowing through the coils (not shown). The magnetic flux flows through write pole 102, and write pole 102 emits a magnetic field across the write gap into perpendicular recording medium 120. The magnetic flux then flows through the SUL 124 and returns to the surface of the disk at a location adjacent to return pole 104. As the magnetic field passes through perpendicular magnetic recording layer 122, the perpendicular component of the magnetic field influences the magnetization orientation of the perpendicular magnetic recording layer 122 in the direction of the magnetic field. The magnetization orientations of three bits in perpendicular magnetic recording layer 122 are illustrated as single arrows pointing up or down in FIG. 1.
When write element 100 is writing to perpendicular recording medium 120, write pole 102 has a leading side 106 and a trailing side 107. To prevent writing to neighboring bits along the track, a trailing shield 108 may be added proximate to the trailing side 107 of write pole 102. The separation between the trailing shield 108 and the write pole 102 is referred to as the shield gap. Trailing shield 107 shunts unwanted magnetic flux from write pole 102.
FIGS. 2-3 illustrate a method 200 of fabricating write poles and trailing shields for perpendicular write elements. FIG. 2 is a flow chart illustrating the method of fabricating, while FIG. 3 illustrates the results of method 200 in forming the layers of the write poles, the trailing shields, etc. Although method 200 described in FIG. 2 applies to wafer-level fabrication, FIG. 3 shows the results for a single perpendicular write element being fabricated on a wafer (not shown). The reference numbers of the steps shown in FIG. 2 are also referenced in FIG. 3.
In step 201, write pole material 301 is deposited (e.g., NiFe, CoNiFe, CoFe, or laminated CoFe/Cr) on the wafer. In step 202, a hard mask 302 is deposited on the write pole material 201. The hard mask 302 may comprise a Thin Alumina Mask (TAM). In step 203, photolithographic soft masks 303 are formed on the hard mask 302 corresponding with the locations of the write poles through deposition and patterning steps. In step 204, ion milling or another similar process is performed on the wafer to remove the write pole material 301 and the hard mask 302 not covered by the soft masks 303. After step 204, write poles 304 remain covered by the hard mask 302 and the soft mask 303. At this point, there may be a targeted re-deposition of the write pole material 301 on the sides of the write pole 304 to achieve a desired shape of the write pole 304. In FIG. 3, the top surface of the write pole 304 comprises the trailing side of the write pole, which is shown as surface 107 in FIG. 1.
In step 205, insulating material 305 (e.g., aluminum oxide) is deposited over the write poles 304, the hard mask 302, and the soft masks 303. In step 206, chemical mechanical polishing (CMP) is performed to a desired depth, which removes some of the insulating material and the soft masks 303. After CMP, notches 306 remain on top of the hard mask 302. In step 207, trailing shield material 307 is deposited to form the trailing shields 308.
One problem with conventional methods of fabrication such as described above is that control of the shield gap between the write pole 304 and the trailing shield 308 may not be as precise as desired. In this fabrication process, the hard mask 302 remains between the write pole 304 and the trailing shield 308. Thus, the thickness of the hard mask 302 defines the shield gap, which may not be as precisely controlled during fabrication as desired.